Continuous slurry dryer

ABSTRACT

This invention relates to an agitating type of dryer for continuously drying high-density slurries with high efficiency. This type of dryer is provided with a large number of paddles radially disposed on a pair of hollow shafts to transport and agitate high-density slurries to be dried in the machine. These shafts rotate in predetermined opposite directions while the paddles are engaging with each other. Each shaft is disposed within a horizontal cylindrical vessel with a jacket. Hot gas passes through the hollow shafts and the jacket, respectively in the direction of slurry flow. Two co-currents of exhaust gas are then combined to pass through the vessel now in the reverse direction until the gas is exhausted from an exhaust port at the front end of the vessel. This type of dryer is capable of drying the high-density slurries which the prior art dryers found it difficult to dry effectively.

United States Patent Kubo [ CONTINUOUS SLURRY DRYER [72] Inventor: Kazunori Kubo, 722-3, Nabaube, Oaza,

Ube-shi, Yamagrichi-ken, Japan [22] Filed: Nov. 24, 1970 [21] Appl. No.: 92,450

[30] Foreign Application Priority Data Nov. 28, 1969 Japan .44/95186 [52] US. Cl ..34/68, 34/182, 34/183, 165/87, 165/92, 241/57, 241/67, 241/113, 241/236, 241/276 [51] Int. Cl ..F26b17/20 [58] Field olSeax-ch ..34/l7, 68, 166, 183, 182,179; 165/87, 92

[56] References Cited UNITED STATES PATENTS 3,426,838 2/1969 Onarheim ..34/183 X 3,581,407 6/1971 Ward et al. ..34/l82 Saxon ..34/182 Napier ..34/182 Primary ExaminerAlbert W. Davis, .Jr.

' Attorney-Kemon, Palmer & Estabrook ABSTRACT This invention relates to an agitating type of dryer for continuously drying high-density slurries with high efficiency. This type of dryer is provided with a large number of paddles radially disposed on a pair of hollow shafts to transport and agitate high-density slurries to be dried in the machine. These shafts rotate in predetermined opposite directions while the paddles are engaging with each other. Each shaft is disposed within a horizontal cylindrical vessel with a jacket. Hot gas passes through the hollow shafts and the jacket, respectively in the direction of slurry flow. Two co-currents of exhaust gas are then combined to pass through the vessel now in the reverse direction until the gas is exhausted from an exhaust port at the front end of the vessel. This type of dryer is capable of drying the high-density slurries which the prior art dryers found it difficult to dry effectively.

4 Claims, 4 Drawing Figures l l l 9 n l l 1: :1 1 l There are two types of conventional continuous dryers: one was the co-current or parallel flow type and the other the countercurrent type in the relative directions to flow the material and the gas. Hence there were various types of dryers manufactured by utilizing their respective characteristics.

There were, however, serious disadvantages. In the countercurrent type, some materials were subjected to thermal decomposition due to heat of the hot gas for drying; these materials were exposed to the hot gas when dehumidified by evaporation because the humid material and the hot gas flowed in opposite directions. It should be noticed, however, that in the case of materials having high thermal decomposition temperatures, this type had the advantage of its high drying efficiency.

In the co-current or parallel flow type, there was the disadvantage that it was inferior to the countercurr'ent type in effi ciency, though less dangerous in thermal decomposition of the material because the hot gas decreased its temperature as the material was dehumidified. Apart from such defects, where chemical reaction must be avoided by direct contact between the material and the gas, drying by indirect heating, though very low in efficiency, must be employed.

Furthermore, in mass production or in the treatment of powder dust or slurries, a continuous drying was necessitated from the standpoint of labor sanitation. In a device for continuously drying viscous materials such as high-density slurries, clay, etc., the paddles radially disposed on the shafts to feed or spoon up the material were seriously damaged by the high-density material sticking thereto. The shafts become thick, thereby causing an abnormal rise in rotating power and frequently incurring troubles and failures. The fact is that there are very few slurry dryers capable of continuous, long operation in the present time.

In the case of low-density materials, there are excellent dryers manufactured according to the princple of fluidized bed dryer. In practical applications, however, there are no slurry dryers capable of continuous, long operation.

SUMMARY OF TI-IE INVENTION Accordingly, an object of the invention is to surmount these disadvantages and provide a continuous slurry dryer capable of effectively drying the material without degenerating it. A more detailed description thereof is now given below. This dryer comprises a pair of hollow shafts rotating in predetermined opposite directions; a large number of paddles radially disposed on each shaft, engaging with each other as the two shafts are rotating; a horizontal cylindrical vessel surrounding the shafts and jacket; means for flowing hot gas into the jacket; means for heating the material in the co-current or parallel flow through the bulkheads; means for combining the Co-currents of hot gas exhausted from the holes of shafts end and opening of the jacket end respectively; and means for heating the material by direct contact with the material in the countercurrent.

This type of dryer is adapted for continuously drying slurries containing moisture, such as gypsum, clay, red mud of alumina refining, ilmeniteresidue of titanium manufacturing, or various kinds of pigments.

The present invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. I is an elevational view of a continuous slurry dryer embodying this invention;

FIG. 2 is a cross-sectional view of the dryer of FIG. 1;

FIG. 3 shows a schematic development in which the curved surface of each shaft is converted into a plane;

FIG. 4A is a partial elevational view illustrating the schematic arrangement of numerous paddles on each shaft of FIG. 3; and

FIG. 4B is a side view of FIG. 4A.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, a more detailed description is given to an embodiment of the invention. In FIGS. I and 2,

the numerals l and 2 designate a pair of hollow shafts. These I shafts rotate in predetermined opposite directions within a hermetically sealed, horizontal, cylindrical vessel 5. This vesse] is supported by two pedestals 21 and 22 and has a heating jacket 6 at the base. FIG. 2 shows a cross section taken along the line X-Y of FIG. 1, illustrating the rotation of each shaft. These two shafts are rotated in opposite directions as shown by the arrows in FIG. 2 so as to allow the paddles (not shown) to shift or spoon up thematerial from between two circles (each represented by an alternate long and short dash line in FIG. 2) and to scatter it outwardly. Paddle tips of each shaft are arrayed on the circumference of each circle. To reverse these directions would press the material against the base of the vessel 5 and this stagnate the current resulting in failures. The material is put in this vessel from a material inlet 10 and is carried forward (from right to left in FIG. 1) by rotation of numerous paddles 25 and 26 implanted on the outer surfaces of the shafts l and 2. Meanwhile, the material is heat dehumidified and exhausted from a product outlet 7 as a finished dried product.

The jacket 6 through which the hot gas flows is disposed at the base of the vessel 5 in the axial direction. This vessel is the principal part of this type dryer. Heart of the parallel flow hot gas through the jacket 6 is transmitted to the material through the inside walls of the vessel 5. It should be noted that the humidity of the hot gas does not increase because there is no direct contact between them.

Part of the hot gas enters the jacket 6 from its inlet 8. Its amount is suitably controlled by a damper 23. The hot gas within the jacket 6 is exhausted from the jacket outlet 12 after transmitting heat to the material as described above, the humidity of the hot gas itself remaining unaltered. This hot gas then flows through the vessel 5 now in the reverse direction as shown by the arrow in FIG. 1, so as to dry the material. To the left from the jacket outlet 12 in FIG. 1 is disposed a single jacket wall leading to the material outlet 7. The paddles are mounted on the shafts I and 2 normally to the axis of each shaft, thereby mainly slicing, shifting and agitating the materi a]. It has been found that there were almost no contents of the material (original slurries) dispersed as dried powder by centrifugal force and that there was almost no powder to block the jacket outlet 12 which was open to the portion consisting of the outside walls only of the jacket 6 by removing the inside walls thereof below the vessel 5. All the dried powder is thus exhausted from the material outlet 7.

While the hot gas for drying is passing through the vessel 5 in the reverse direction, as described above, buffer plates 13 are mounted on the ceiling of the vessel 5 to divide the interior of the vessel into three equal sections longitudinally of the ves' sel, permitting the current to be agitated vertically and thus improving contact between the hot gas and the slurry material.

The countercurrent of hot gas now at a considerably low temperature transmits heat by direct contact with the material continuously inserted from its inlet 10. The gas is exhausted from the exhaust port 9 to the external atmosphere after satisfactorily drying the material.

Part of the hot gas introduced from its inlet 8 is delivered to the jacket 6 through the damper 23, as described above. The remainder is flowed into the two hollow shafts 1 and 2 through a sliding coupling 14. The heat of the hot gas passing through these two hollow shafts and the jacket 6 is transmitted to the material through the shaft walls and jacket walls.

Paddles 25, 26 and 27 shown in FIGS. 3 and 4 are radially disposed on the surfaces 24 of the shafts l and 2, to transport, slice, shift and agitate the material. These paddles finally serve to feed the material. It should be noticed that the angle of paddles varies with the properties and humidity of the material. Part of the hot gas flowing into the hollow shafts l and 2 is exhausted from its shaft outlet 11 within the vessel 5 and is combined with the remainder exhausted from its jacket outlet 12.

FIG. 3 shows the arrangement of numerous paddles 25 on an imaginary plane corresponding to the curved surface of each of the shafts l and 2 within the vessel 5. These paddles are radially disposed on the shafts l and 2 respectively, each at an incline of several, preferably about 5 degrees, relative to the direction normal to the axis of shaft rotation. Rotation of these shafts carries the material forward (from right to left in FIG. I). As described above, the incline and direction of each paddle and the number of paddles vary with the properties and humidity of the material. Many other paddles 26 are radially disposed on each shaft normally to the axis of shaft rotation. These paddles serve to slice the material to be dried within the vessel 5, but not to feed it. Spatulate type paddles 27 at the end portion of each shaft serve to ladle up the material as the shaft rotates, thereby effectively exhausting the dried, powdered material from its outlet 7. FIG. 4 shows some paddles embodying the invention. Paddles 25 and 26 are the flat bar type steel plates welded on the shaft (FIG. 4A). Paddle 27 is of the spatulate type (FIGS. 4A and 4B). This paddle 27 is bent at the tip of the plate, thereby spooning up the material.

There shafts each with numerous paddles are supported by a supporting bearing 20 through bearings and 16 so as to rotate in prescribed opposite directions. A spur gear 18 having the same number of teeth is disposed at the end portion 7 of one shaft so as to allow the two shafts to engage with each other. This gear is rotated by geared motor or the like through a chain wheel 19 mounted on one of the shafts.

As shown in FIG. 3, location of the numerous paddles radially disposed on the shafts l and 2 respectively is adjusted in such a manner that when these shafts are rotating in prescribed opposite directions the paddles of one shaft intermesh those of the other to prevent mutual collision.

FIG. 2 shows two circles each represented by an alternate long and short dash line in FIG. 2 illustrating how the paddles (not shown) intermesh with each other while the shafts are rotating in prescribed opposite directions, thereby preventing the material from sticking to the shafts and paddles to some extent. Therefore, the slurry dryer of the invention is hardly affected by the tendency of the slurry material to stick to the shafts and paddles during drying. Thus this dryer is capable of drying the slurry material continuously for a long time, in good order, and at high efficiency.

In the dryer of the invention, the gas at high temperatures transmits heat as co-current or parallel flow, whereas the gas at relatively low temperatures transmits heat as countercurrent by direct contact with the material. Therefore the slurry dryer of the invention is well adapted for drying otherwise difficulty dried materials, such as high-density slurries, without any change in quality and at high drying efieciency.

EXAMPLE Size of the cylindrical vessel 5 in FIG. l

Length: 1,885 mm. Height: 685 mm. Bore: 570 mm. Outside diameter of each shaft: I40 mm. Diameter of a circle formed by rotation of a paddle up: Number and direction of paddles:

' Same as those of FIG. 3

These two shafts were rotated at 20 r.p.m. by a reduction gear with a 2.5 kilowatt motor in the opposite directions shown by the arrows in FIG. 2.

Light oil of 4.68 l/h (heating value of 9,000 cal/kg) was burned to obtained a hot gas. When introduced into the dryer, the temperature of this hot gas was 235C at its inlet, 133C at its shaft outlet 11, and 94C at its vessel outlet 9. The ilumenite slurrieshavin moisture content of 40.5 percent at 18C were continuous y feed mto the material inlet 10 at the rate of 84 kg/h for drying. These slurries were then exhausted from the material outlet 7. In this case the moisture content was 9.8 percent and the temperature was 40C at outlet 7. The slurry material so dried was exhausted from the material outlet 7 at the rate of 6S kg/h.

Meanwhile, the machine operated for 6 continuous hours without any failure, thereby obtaining the dried articles of practically the same quality at all times. The thermal efficiency during drying was 52 percent.

What is claimed is:

l. A horizontal type, jacketed, continuous cylindrical slurry dryer adapted to agitate, slice and feed a moisture-containing slurry material comprising:

1. a horizontal cylindrical vessel including a front end, a rear end, a bottom portion, heating jacket with an inlet and an outlet on said bottom portion, a material inlet at said front end and a material outlet at said rear end;

2. a pair of hollow shafts horizontally mounted within said vessel for rotation by an external means, one being rotated in a clockwise direction, the other in a counterclockwise direction;

. a plurality of agitating and transmitting paddles radially mounted on each shaft to permit the paddles on one shaft to intersect the paddles on the other shaft upon rotation of the shafts;

said paddles being radially arranged on the shaft, some at a right angle to the shaft axis and some at an acute angle to the shaft axis;

5. hot gas inlet means on said front end at the vessel including divided passage to direct a first portion of hot gas in a direction co-current to the direction of the flow of the slurry material charged into the vessel to flow through the interior of said jacket from an outlet in the jacket in the region of said material outlet, from which it is introduced into the interior of the vessel to flow in a direction counter-current to the direction of the flow of the slurry material to permit dehydration through direct contact with the slurry material and be discharged from a gas outlet disposed in said vessel at said front end; and

6. a second portion of hot gas in a direction co-current to the direction of the flow of the slurry material to flow through the interior of said hollow shafts to permit the slurry material to be dehydrated through indirect contact with the heated shaft walls, the exhaust gas of which is discharged from a shaft outlet disposed above said material outlet to cause it to meet said first portion of hot gas and flow in a direction countercurrent to the direction of the flow of the slurry material in direct contact with the slurry material; and

7. means to control division of said hot gas into said first and second portions.

2. The slurry dryer according to claim I, wherein paddles mounted radially on the respective shafts are declined at a feed angle of about 5 to the direction vertical to the shaft axis to permit the slurry material to be fed to the outside upon rotation of the respective shafts.

3. The slurry dryer according to claim 1, wherein said dryer includes a plurality of bufier plates mounted on the inner wall of the vessel longitudinally of the vessel to divide the interior of the vessel into three sections.

4. The slurry dryer according to claim 1, wherein paddles adjacent to the respective shaft outlets are in the form of spatula.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. a 596 Dated July 1972 lnvent r( Kazunori'Kubo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

First Page Address of inventor 722-3, Nabau'be,

Gaza, Ube-shi, Yamagric'hi-ken, Japan replace with:

.-722-3, Nakaube Oaza, U'be-shi Yamaguchi-ken, Japan-- Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM (10459) USCO MM-DC sows-ps9 it [L5, GQVERNMENT PRINTING OFFICE 199 0-366-334 

1. A horizontal type, jacketed, continuous cylindrical slurry dryer adapted to agitate, slice and feed a moisture-containing slurry material comprising:
 1. a horizontal cylindrical vessel including a front end, a rear end, a bottom portion, heating jacket with an inlet and an outlet on said bottom portion, a material inlet at said front end and a material outlet at said rear end;
 2. a pair of hollow shafts horizontally mounted within said vessel for rotation by an external means, one being rotated in a clockwise direction, the other in a counter-clockwise direction;
 3. a plurality of agitating and transmitting paddles radially mounted on each shaft to permit the paddles on one shaft to intersect the paddles on the other shaft upon rotation of the shafts;
 4. said paddles being radially arranged on the shaft, some at a right angle to the shaft axis and some at an acute angle to the shaft axis;
 5. hot gas inlet means on said front end at the vessel including divided passage to direct a first portion of hot gas in a direction co-current to the direction of the flow of the slurry material charged into the vessel to flow through the interior of said jacket from an outlet in the jacket in the region of said material outlet, from which it is introduced into the interior of the vessel to flow in a direction counter-current to the direction of the flow of tHe slurry material to permit dehydration through direct contact with the slurry material and be discharged from a gas outlet disposed in said vessel at said front end; and
 6. a second portion of hot gas in a direction co-current to the direction of the flow of the slurry material to flow through the interior of said hollow shafts to permit the slurry material to be dehydrated through indirect contact with the heated shaft walls, the exhaust gas of which is discharged from a shaft outlet disposed above said material outlet to cause it to meet said first portion of hot gas and flow in a direction countercurrent to the direction of the flow of the slurry material in direct contact with the slurry material; and
 7. means to control division of said hot gas into said first and second portions.
 2. a pair of hollow shafts horizontally mounted within said vessel for rotation by an external means, one being rotated in a clockwise direction, the other in a counter-clockwise direction;
 2. The slurry dryer according to claim 1, wherein paddles mounted radially on the respective shafts are declined at a feed angle of about 5* to the direction vertical to the shaft axis to permit the slurry material to be fed to the outside upon rotation of the respective shafts.
 3. The slurry dryer according to claim 1, wherein said dryer includes a plurality of buffer plates mounted on the inner wall of the vessel longitudinally of the vessel to divide the interior of the vessel into three sections.
 3. a plurality of agitating and transmitting paddles radially mounted on each shaft to permit the paddles on one shaft to intersect the paddles on the other shaft upon rotation of the shafts;
 4. said paddles being radially arranged on the shaft, some at a right angle to the shaft axis and some at an acute angle to the shaft axis;
 4. The slurry dryer according to claim 1, wherein paddles adjacent to the respective shaft outlets are in the form of spatula.
 5. hot gas inlet means on said front end at the vessel including divided passage to direct a first portion of hot gas in a direction co-current to the direction of the flow of the slurry material charged into the vessel to flow through the interior of said jacket from an outlet in the jacket in the region of said material outlet, from which it is introduced into the interior of the vessel to flow in a direction counter-current to the direction of the flow of tHe slurry material to permit dehydration through direct contact with the slurry material and be discharged from a gas outlet disposed in said vessel at said front end; and
 6. a second portion of hot gas in a direction co-current to the direction of the flow of the slurry material to flow through the interior of said hollow shafts to permit the slurry material to be dehydrated through indirect contact with the heated shaft walls, the exhaust gas of which is discharged from a shaft outlet disposed above said material outlet to cause it to meet said first portion of hot gas and flow in a direction countercurrent to the direction of the flow of the slurry material in direct contact with the slurry material; and
 7. means to control division of said hot gas into said first and second portions. 